Color reproducing device

ABSTRACT

In a color reproduction device, an input profile that is referenced in converting an input image from an image input device into a device-independent color image is created based on image input device information, shooting- and observation-time lighting data, and subject data, allowing accurate conversion of the input image to the device-independent color image. In reproducing the image by an image output device, the spectral reflectance of the subject itself is calculated from image input device information and shooting-time lighting data, thereby reducing the effect of the shooting-time lighting. The colors of the subject under observation lighting are calculated from observation-time lighting data. A color reproduced image is estimated accurately on the basis of the subject data even if the input image has little information.

This is a division of U.S. patent application Ser. No. 09/149,906 filedSep. 8, 1998, now U.S. Pat. No. 6,466,334.

BACKGROUND OF THE INVENTION

The present invention relates to a color reproducing device whichtransfers accurately the colors of an image of a subject captured by animage input device to an output device.

Various attempts have been made hitherto to print or display colors asthey are perceived by the human visual system.

As the performance of computers has been upgraded and their size hasbeen reduced and with the spread of desktop publishing (DTP) systems,color matching techniques have been proposed for matching colorsdisplayed on TV monitors and colors to be printed on printed matter asan object of input and output (for example, U.S. Pat. No. 5,739,928,Japanese Unexamined Patent Publication No. 6-51732, and so on).

A color management system (CMS), which is typical of the color matchingtechniques, is equipped, as shown in FIGS. 32 and 33, with a colorcorrector 3 between an image input device 1 and an image output device2. The color corrector 3 has an input profile 4 and an output profile 5on the image input side (shooting side) and the image output side(observer side), respectively. Input colors are first converted tocolors that do not depend on the image input device 1 and the imageoutput device 2 (hereinafter referred to as device independent colors)and then the matching of input and output colors is performed.

In U.S. Pat. No. 08/763,230, there is disclosed a color image recordingand reproducing system in which, as shown in FIG. 34, an image capturedin a place remote from a place where it is reproduced is transmitted,and color matching is performed in spectrum to reproduce (display orprint) colors accurately.

More specifically, in this system, a multi-spectral image of a subjectis shot, and lighting spectral data when the image was shot and lightingspectral data at the time the image is reproduced are used to effectconversion in such a way that, under lighting on the reproduction side,the spectral image of the subject is obtained as it was shot.

That is, the colors and gloss of the subject when it was shot arechanged to suit the reproducing lighting, allowing the state of thesubject when it was shot to be observed.

Next, a multidimensional spectral image is converted into athree-dimensional vector image composed of X, Y, and Z values and thentransmitted to the reproducing site. In the reproducing site, the imageis converted to color signals corresponding to the spectralcharacteristics of the reproducing device and then outputted to adevice.

The color corrected image is displayed on an output medium (monitor) ofFIG. 34.

The output profile is created in accordance with the followingprocedure.

A monitor 131 and a chromaticity meter 132 are set in a place, such as adark room, which is not affected by outside light. As shown in FIG. 35,predetermined RGB signals are generated by an RGB signal generator 133and displayed on the screen of the monitor under the control of adisplay controller 134. The colors displayed are measured by thechromaticity meter 132.

The output signals of the chromaticity meter 132 are detected by achromaticity detector 135 as chromaticity values such as XYZ values. Thedetected signals are then sent to an output profile computation unit136.

The output profile computation unit computes an output profile from therelationship between the RGB values generated by the RGB signalgenerator 133 and the chromaticity valued detected by the chromaticitymeter 135.

The relationship between the RGB values outputted to the monitor 131 andthe XYZ values outputted from the monitor 131 will be described next.

The monitor has RGB phosphors that produce the three primary colors,red, green, and blue, and produces a color image by exciting thosephosphors by electron beams modulated by R, G and B signals. The valuesof the R, G and B signals (the RGB values) are produced by the RGBsignal generator 133 of FIG. 35.

The RGB values are converted in a non-linear manner by the gamma (γ)characteristic of the monitor 131. Let the gamma characteristic of theRGB phosphors be denoted by γr[ ], γg[ ], and γb[ ], respectively. Thecolors produced by the RGB phosphors are combined by eye into a color;thus, the chromaticity values (XYZ values) outputted from the monitorare represented by the sums of signal values each subjected to thecorresponding gamma characteristic as follows: $\begin{matrix}{\begin{pmatrix}X \\Y \\Z\end{pmatrix} = {\begin{pmatrix}{{Xr}\quad\max} & {{Xg}\quad\max} & {{Xb}\quad\max} \\{{Yr}\quad\max} & {{Yg}\quad\max} & {{Yb}\quad\max} \\{{Zr}\quad\max} & {{Zg}\quad\max} & {{Zb}\quad\max}\end{pmatrix}\begin{pmatrix}{\gamma\quad{r\lbrack R\rbrack}} \\{\gamma\quad{g\lbrack G\rbrack}} \\{\gamma\quad{b\lbrack B\rbrack}}\end{pmatrix}}} & (11)\end{matrix}$where Xrmax, Yrmax and Zrmax are the X, Y and Z values when the Rphosphor produces the maximum brightness, Xgmax, Ygmax and Zgmax are theX, Y and Z values when the G phosphor produces the maximum brightness,and Xbmax, Ybmax and Zbmax are the X, Y and Z values when the B phosphorproduces the maximum brightness.

The RGB values to obtain desired XYZ values can be calculated usingequation (11) as follows: $\begin{matrix}\begin{matrix}{{{matrix}\quad{transform}\quad\begin{pmatrix}R^{\prime} \\G^{\prime} \\B^{\prime}\end{pmatrix}} = {\begin{pmatrix}{{Xr}\quad\max} & {{Xg}\quad\max} & {{Xb}\quad\max} \\{{Yr}\quad\max} & {{Yg}\quad\max} & {{Yb}\quad\max} \\{{Zr}\quad\max} & {{Zg}\quad\max} & {{Zb}\quad\max}\end{pmatrix}^{- 1}\begin{pmatrix}X \\Y \\Z\end{pmatrix}}} \\{{gamma}\quad{correction}\quad\begin{matrix}{R = {\gamma\quad{r^{- 1}\left\lbrack R^{\prime} \right\rbrack}}} \\{G = {\gamma\quad{g^{- 1}\left\lbrack G^{\prime} \right\rbrack}}} \\{B = {\gamma\quad{b^{- 1}\left\lbrack B^{\prime} \right\rbrack}}}\end{matrix}}\end{matrix} & (12)\end{matrix}$

The processing flow is illustrated in FIG. 36.

In this arrangement, an output profile computation unit 136 computesmatrix coefficients for matrix transform and gamma correction values forgamma correction from the RGB values and the XYZ values and stores theminto an output profile storage unit 137. A device value conversion unit138 makes matrix transform and gamma correction on the XYZ values usingthe matrix coefficients and the gamma correction values and outputs RGBvalues to the image display controller 134 for display on the monitor.

The conventional color management system described above specifies D50for the light source used on both the input side and the output side.Therefore, a color mismatching problem will arise when an image is shotunder a light source different from D50 or when an output image isobserved under a light source different from D50.

In the conventional color image recording and reproducing systemillustrated in FIG. 34, it is assumed that, on the shooting side, animage is converted to chromaticity values, such as XYZ values, to suitthe lighting on the observer side and then transmitted to the observerside.

An image, once converted to XYZ values, has no longer spectralinformation. Thus, on the observer side, no data conversion can be madeto suit the lighting.

Only the spectral data on light used in shooting and the spectral dataon light used in observation are used for color matching. In order toincrease the accuracy of color reproduction, therefore, it is requiredthat an input image itself should have a certain amount of spectralinformation.

For this reason, the image input device must be a multi-spectral cameracapable of capturing spectral images in many bands, which makes itdifficult to shoot a subject in one shot. In addition, a captured imagewill involve a large amount of data.

In displaying a color corrected image on the monitor, offset light(light of monitor emitted when the input value is zero) and environmentlight (light of surrounding place where the monitor is installed) willhave influence on color reproduction. Thus, satisfactory colorreproduction is not necessarily achieved even if an output profile iscreated for the monitor by the conventional technique.

When the power is applied to the monitor and then RGB signals such thatR=G=B=0 are applied to the monitor, the monitor screen will not displayblack (X=Y=Z=0) due to the influence of offset light of the monitor.

In a place where the monitor is set, there generally exists some lightsource or outdoor light (sun light) which illuminates the monitorscreen. Under such conditions, reflection from the monitor screen occursand hence it does not follow that X=Y=Z=0 even when the power is notapplied to the monitor. That is, the monitor offset light and theenvironment light are added to an image to be displayed on the monitor.The sum of the monitor offset light and the environment light isreferred hereinafter to as a bias value.

If a profile is created taking the bias value into account, thenaccurate color reproduction will be achieved. However, the offset lightand the environment light vary greatly with time. For example, theoffset light varies greatly until the monitor becomes stabilized fromwhen the power was applied thereto.

In addition, the bias value will vary greatly when a light source usedas environment light is changed, or subjected to a change with thepassage of time, or the outdoor light varies. The recreation of theoutput profile with each variation of the offset light or environmentlight requires not only expert knowledge but also a large amount oftime.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a color reproductiondevice which makes image conversion while referencing image input deviceinformation, and color reproduction environment information containingshooting- and observation-time lighting spectral information andinformation concerning the statistical nature of the spectrum of asubject, allows the image shooting and reproducing sites to be remotefrom each other, and allows accurate color reproduction even when offsetlight and environment light vary.

To attain the object, there is provided a color reproduction device foroutputting an image of a subject shot by an image input device to animage output device in displayed or printed form, which comprises aninput profile creation section for creating an input profile thatconforms to information concerning the image input device andenvironment information containing shooting- and observation-timelighting data and information concerning the optical nature of thesubject, a device-independent color conversion section having an inputprofile operation section for causing the input profile to operate onthe image to convert it to a device-independent color image, and adevice value conversion section for causing an output profile created inaccordance with information concerning the image output device tooperate on the device-independent color image to convert it to devicevalues.

Additional objects and advantages of the invention will be set forth inthe description which follows, and in part will be obvious from thedescription, or may be learned by practice of the invention. The objectsand advantages of the invention may be realized and obtained by means ofthe instrumentalities and combinations particularly pointed outhereinafter.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate presently preferred embodiments ofthe invention, and together with the general description given above andthe detailed description of the preferred embodiments given below, serveto explain the principles of the invention.

FIG. 1 is a schematic illustration of a first embodiment of a colorreproduction device of the present invention;

FIG. 2A show arrangements of the device-independent color conversionunit, respectively, of FIG. 1;

FIG. 2B show arrangements of the device value conversion unit,respectively of FIG. 1;

FIG. 3 shows another arrangement of the color correction unit of FIG. 1;

FIG. 4 shows an arrangement of the device independent color conversionunit;

FIG. 5 is a diagram for use in explanation of a way of inputtingenvironmental information to the correction unit;

FIG. 6 is a diagram for use in explanation of a way of inputtingenvironmental information to the correction unit;

FIG. 7 shows an arrangement of the color correction unit which isseparated into a color correction preprocessing unit and a colorcorrection postprocessing unit;

FIG. 8 shows an arrangement for creating an input/output profile byconcatenating an input profile and an output profile;

FIG. 9 shows a specific arrangement of the color reproduction deviceaccording to the first embodiment;

FIG. 10 is a schematic illustration of a second embodiment of the colorreproduction device of the present invention;

FIG. 11 is a diagram for use in explanation of lighting convertibleimage data which is inputted to a color correction unit of a deviceaccording to a third embodiment;

FIG. 12 shows a format of lighting convertible image data used in thethird embodiment;

FIG. 13 shows a modification of the third embodiment;

FIG. 14 shows a format of lighting convertible image data used in themodification of the third embodiment;

FIG. 15 shows, in appearance form, a first specific application of thedevice according to the third embodiment;

FIG. 16 shows, in block diagram form, an arrangement of the device ofFIG. 15;

FIG. 17 shows, in appearance form, a second specific application of thedevice according to the third embodiment;

FIG. 18 shows, in block diagram form, an arrangement of the digitalcamera of FIG. 17;

FIG. 19 shows, in block diagram form, an arrangement of the device ofFIG. 17;

FIG. 20 shows an arrangement of a multi-spectral camera used in a fourthembodiment of the color reproduction device of the present invention;

FIG. 21 shows a second arrangement of the multi-spectral camera used inthe fourth embodiment of the color reproduction device of the presentinvention;

FIG. 22 shows an arrangement of a multi-spectral camera used in a fifthembodiment of the color reproduction device of the present invention;

FIG. 23 shows an arrangement of the device value conversion unit in asixth embodiment of the color reproduction device of the presentinvention;

FIG. 24 is a conceptual diagram of the monitor screen in a seventhembodiment of the color reproduction device of the present invention;

FIGS. 25A, 25B and 25C shows the measurements of bias values using achromaticity meter in different environments in the seventh embodiment;

FIG. 26 shows an arrangement of the device value conversion unit in theseventh embodiment of the color reproduction device of the presentinvention;

FIGS. 27A and 27B are diagrams for use in explanation of a chromaticitysensor used in an eighth embodiment of the present invention;

FIGS. 28A, 28B and 28C show modifications of the chromaticity sensor inthe eighth embodiment;

FIG. 29 shows an arrangement of a ninth embodiment of the colorreproduction device of the present invention;

FIG. 30 shows an arrangement of a tenth embodiment of the colorreproduction device of the present invention;

FIG. 31 shows an arrangement of the device value conversion unit in aneleventh embodiment of the color reproduction device of the presentinvention;

FIG. 32 is a schematic illustration of a conventional color reproductiondevice;

FIG. 33 shows an arrangement of the color correction unit in theconventional color reproduction device;

FIG. 34 shows an arrangement of a conventional color reproduction devicein which a shooting site and a reproduction site are remote from eachother;

FIG. 35 shows an arrangement of the output profile creation unit in thecolor correction unit in the conventional color reproduction device; and

FIG. 36 shows an arrangement for performing a sequence of processes ofmatrix transform and gamma correction in the color correction unit inthe conventional color reproduction device.

DETAILED DESCRIPTION OF THE INVENTION

Reference will be made to FIGS. 1 through 7 to describe a firstembodiment of a color reproduction device of the present invention.

As shown in FIG. 1, the color reproduction device is composed roughly ofan image input device 1 for capturing an image of a subject, a colorcorrection unit 3 for correcting the colors of the image, and an imageoutput device 2 for outputting (displaying or printing) an output image.

The color correction unit 3 is composed of a device independent colorconversion unit 4 and a device value conversion unit 5.

The device independent color conversion unit 4 converts the colors of aninput image to device independent colors by making a reference to aninput profile 4 a, thereby producing a device independent color image.The device value conversion unit 5 makes a reference to an outputprofile 5 a to convert the device independent color image to an outputimage that have values that match the characteristics of the imageoutput device 2.

The device independent color conversion unit 4 is constructed, as shownin FIG. 2A, from an input profile creation unit 6 and an input profileoperation unit 7. The input profile creation unit 6 is responsive toimage input device information and environmental information about acolor reproduction environment to create and output an input profile 4 ato the input profile operation unit 7. The operation unit 7 causes theinput profile to operate on the input image to provide image colorconversion.

As shown in FIG. 4, the input profile creation unit 6 may be arranged asa matrix creation unit 9 and the input profile operation unit 7 may bearranged as a matrix operations unit 8. Thus, since an input profile canbe created by means of matrix operations, an input image can beconverted into a device-independent color image at high speed.

The color correction unit 3 includes, as shown in FIG. 3, aninput/output profile creation unit 11 and an input/output profileoperation unit 13 to create an input/output profile 12 from the inputprofile 4 a and the output profile 5 a. In this manner, the inputprofile 4 a and the output profile 5 a can be concatenated to make fastconversion from an input image to an output image.

The input profile creation unit 6, which creates an input profile takinginto account various items of information for creating a colorreproduced image, can convert an input image to a device-independentcolor image with accuracy.

The image input device information shown in FIG. 2 contains thecharacteristics of the image input device used in shooting and settingstates (hereinafter referred to as shooting characteristics). On theother hand, the environment information contains spectral dataconcerning lighting used in capturing an image of a subject with theimage input device (hereinafter referred to as shooting-time lightingdata), spectral data concerning a light source in the place where theimage of the subject is watched (hereinafter referred to asobservation-time lighting data), and information concerning thestatistical nature of the spectrum of the subject which was shot(hereinafter referred to as subject characteristics).

The use of the shooting characteristics permits a color reproduced imageof the subject shot by the image input device to be estimated withaccuracy. Even if the image input device is a multi-spectral camera thatcaptures a plurality of spectral images of a subject or a digitalcamera, color reproduction can be achieved.

The use of the shooting-time lighting data permits the effect oflighting at the shooting time to be canceled. That is, even if a subjectis shot under any lighting (for example, fluorescent lamp, incandescentlamp, sunlight, and so on), the accurate spectral reflectance of thesubject itself can be calculated. Also, the use of the observation-timelighting data permits colors under lighting in the place where thesubject image is actually watched to be calculated. The use of thesubject characteristics permits a color reproduced image to be estimatedwith accuracy even if an input image has little spectral information.

Next, the environmental information entered into the color correctionunit 3 will be described with reference to FIGS. 5 and 6.

The environmental information is provided from the image input device 1,a dedicated input device 14, a network 15, or a storage medium 16.

When the environmental information is input from the image input device1 or another input device, shooting-time environmental information canbe obtained in real time, which, even when the environment varies fromhour to hour, allows an input profile that provides accurate conversionto a device-independent color image to be created.

Where the environmental information is provided from the network 15 orthe storage medium 16, an input profile can be created to suit theenvironment at the remote site or the past environment.

As shown in FIG. 6, the color correction unit 3 is composed roughly ofthe device-independent color conversion unit 4 and the device valueconversion unit 5.

The input profile creation unit 6 in the device-independent color imageconversion unit 4 comprises an lighting data select unit 18, a subjectcharacteristic select unit 19, a shooting characteristic select unit 20,and an input profile calculation unit 21.

The lighting data select unit 18, the subject characteristic select unit19, and the shooting characteristic select unit 20 receive image inputdevice information and environment information from the input device 14or the like. The input profile calculation unit 21 calculates inputprofile 4 a based on the outputs of the select units. The input profileoperation unit 7 is composed of an input image select unit 22 whichmakes a selection among input images and a color conversion unit 23which converts the selected image to a device-independent color image onthe basis of the input profile 4 a.

An output profile operation unit 24 in the device value conversion unit5 comprises a color conversion unit 25 which performs a color conversionprocess on the device-independent color image on the basis of the outputprofile 5 a to provide an output image, and an output device select unit26 which selects an output device to which the output image is to bedirected and then directs the output image to either image output device17, storage medium 16, or network 15.

The output profile creation unit 10 for creating the output profile 5 ais composed of an output device characteristic select unit 27 whichselects necessary information from output device information and anoutput profile calculation unit 28 which calculates the output profile 5a based on the selected output device characteristics.

The components in the present embodiment may be subjected to variousmodifications and variations.

For example, the image input device 1 may be a multi-spectral camerausing a plurality of bandpass filters, a multi-spectral camera using awavelength-variable filter using liquid crystals, a multi-spectralcamera in which an optical path is split by means of prisms, or adigital camera. The image output device 17 may be either a TV monitor, aprojector, or a printer.

To obtain spectral data, a spectroscope or multi-spectral camera can beused as the input device 14. The same system may be installed at aremote site on the network 15 for transmission of images andenvironmental information between the systems. As the storage medium,use is made of a floppy disk, a magneto-optical (MO) disk, or the like.

In such an arrangement, as shown in FIG. 7, the color correction unit 3may be separated into a color correction preprocessing section 3 a and acolor correction postprocessing section 3 b. In this case, an outputdevice for a device-independent color image from the color conversionunit 23 is selected by the output device select unit 31 in thepreprocessing section 3 a and then sent to the postprocessing section 3b via a storage medium 29 or a network 30. A selection is made by thedevice independent color image select unit 32 in the output profileoperation unit 24, and the selected image is subjected to colorconversion based on the output profile 5 a in the color conversion unit25.

This embodiment is sometimes effective in storing or transmitting imagedata because the device-independent color image requires a smaller datasize than images in a format that allows lighting conversion. In FIG. 7,corresponding parts to those in FIG. 5 are denoted by like referencenumerals and descriptions thereof are omitted.

Next, an arrangement in which the input profile 4 a and the outputprofile 5 a are combined into an input/output profile 12 will bedescribed with reference to FIGS. 8 and 3.

The input/output profile operation unit 13 in the color correction unit3 comprises an input image select unit 33 which makes a selection amonginput images and an input image conversion unit 34 which converts aselected input image based on the created input/output profile 12. Theimage subjected to conversion is directed to an output device selectedby an image output device select unit 35.

Such an arrangement requires that an input image be subjected toconversion one time only, thus further increasing the processing speedas compared with the arrangement of FIG. 6.

FIG. 9 shows a specific arrangement of the color reproduction deviceaccording to the first embodiment of the present invention. Thisembodiment, implemented in computer software, is an example of a systemarranged to produce and display a color reproduced image on a monitor.

As shown in FIG. 9, this system is composed of a multi-spectral camera41 which captures multi-spectral images of a subject 53, spectrometers42 and 43, a monitor 44, a chromaticity meter 45 for measuring theprofile of the monitor 44, and a computer 46.

Of the sections implemented in software in the computer 46, thosefunctioning in the same way as those shown in FIG. 6 will be designatedat the same reference numerals as used in FIG. 6.

The computer 46 includes, in addition to the sections (software) forcreating an input profile and an output profile, a multi-spectral imageshooting section 47 for capturing images by the multi-spectral camera41, a lighting data measurement section 48 for controlling thespectrometers 42 and 43 to obtain lighting data used for creating theinput profile 4 a, a monitor measurement section 49 for controlling thechromaticity meter 45 to obtain monitor data used for creating theoutput profile 5 a, and a color reproduced image display section 50 fordisplaying a color reproduced image on the monitor 44.

Such an arrangement requires to create the input and output profilesprior to a color reproduced image producing process.

In creating an input profile, shooting-time and observation-timelighting spectral data are measured using spectrometers 42 and 43. Eachof reference plates 51 and 52 used for measurement is simply a platewhose spectral reflectance is already known in order to get exactlighting spectral data. It is preferable to use a plate, such as astandard white plate, that has constant and high spectral reflectance,and little changes in characteristics with the passage of time.Although, in FIG. 9, there are illustrated an electric light bulb as ashooting light source and a fluorescent lamp as an observation lightsource, light sources of the same type may be used. Measurement may bemade using sunlight as opposed to artificial light.

The shooting characteristics of the multi-spectral camera 41 calculatedfrom the lighting data measured by the lighting data measurement section48, and the subject characteristics are entered into the input profilecreation section 6 to create an input profile 4 a. The created inputprofile may be stored on a memory or disk not shown, in which case itwill be read into the computer when it is needed.

The output profile 5 a can be created by displaying appropriate colorson the monitor 44 and measuring them with the chromaticity meter 45.More specifically, the chromaticity values of the phosphors of themonitor 44 and a relationship between digital values for RGB signalsinput to the monitor and actual brightness value (generally known asgamma characteristic) are calculated.

The output profile 5 a is created by the output profile creation section10 on the basis of data measured by the monitor measurement section 49.Like the input profile 4 a, the created output profile 5 a is stored ona memory or disk and read into the computer when needed.

In this embodiment, a chromaticity meter is provided for monitormeasurement; otherwise, the spectrometer for measuring lighting may beused as a chromaticity meter as well.

To produce a color reproduced image of a subject, the subject 53 is shotby the multi-spectral camera 41 and the resultant subject image isoperated on by the input profile 4 a and the output profile 5 a insequence to produce an image that suits the characteristics of themonitor 44. The multi-spectral camera may be either a multi-spectralcamera that has a rotating color filter composed of a plurality ofbandpass filters or a multi-spectral camera that uses a transmittedwavelength-variable filter.

When the input profile 4 a is so designed as to processthree-dimensional data, a normal RGB camera or digital camera can alsobe used.

In the present embodiment, the color reproduction device is implementedby a single personal computer. A color reproduction device or system canalso be implemented which transmits accurately colors among multiplepersonal computers connected to a network.

Hereinafter, an example of an algorithm for software processing will bedescribed. First, let an output signal of the multi-spectral camera bedenoted by gi. Then, gi is represented bygi=∫e _(m)(λ)·f(λ)·h _(i)(λ)·dλ  (1)where em(λ) is the spectrum of shooting lighting, f(λ) is the spectralreflectance, and hi(λ) is the multi-spectral camera sensitivity whenfilter i is used. Actually, the tristimulus values, X, Y, Z, when asubject is observed by human are given byX=∫e ₀(λ)·f(λ)·x(λ)·dλY=∫e ₀(λ)·f(λ)·y(λ)·dλZ=∫e ₀(λ)·f(λ)·z(λ)·dλ  (2)where e₀(λ) is the lighting spectrum at the time of observation, f(λ) isthe spectral reflectance of the subject, and x(λ), y(λ), and z(λ) areeach an isochromatic function. A matrix M is then calculated to satisfyM·g=[X, Y, Z] ^(t)  (3)where t represents the transpose of a matrix.

An evaluation function designs M so as to minimizee ² =E[(X−M·g)²]  (4)where E[ ] represents an operator for seeking an expected value.

M sought as∂e ² /∂M=0  (5)is the least square filter given byM=A·B ⁻¹A _(ij) =∫∫e ₀(λ)·x _(i)(λ)·E[f(λ)·f(λ′)]·e _(m)(λ′)·h _(j)(λ′)·dλ·dλ′B _(ij) =∫∫e _(m)(λ)·h _(i)(λ)·E[f(λ)·f(λ′)]·e _(m)(λ′)·h_(j)(λ′)·dλ·dλ′  (6)

E[f(λ)·f(λ′)] in equation (6) represents a spectral correlation term ofthe subject to be measured. To minimize the evaluation function forevery possible objects, spectral correlation term will be a unit matrix.Therefore matrix M is given byM=A·B ⁻¹A _(ij) =∫e ₀(λ)·x _(i)(λ)·e _(m)(λ)·h _(j)(λ)·dλB _(ij) =∫e _(m)(λ)² ·h _(i)(λ)·h _(j)(λ)·dλ  (7)

If some restrictions are imposed on subjects to be reproduce, and thespectral reflectance of the subject can be represented by some principlecomponents, colors can be estimated with accuracy even from a smallnumber of spectral images. For example, in the field of remote medicalsystems, when the spectral reflectance of skin is measured and acorrelation matrix is then calculated as the statistical nature, theskin color can be reproduced with accuracy from a small number ofspectral images.

That is, for color reproduction processing using subjectcharacteristics, the creation of an input profile corresponds to thecalculation of equation (6). When no subject characteristics are used,the input profile creation corresponds to the calculation of equation(7). The input profile operation section multiplies signals obtained inthe multi-spectral image shooting section by filter M, namely,calculates equation (3).

Next, a second embodiment of the color reproduction device of thepresent invention will be described.

As shown in FIG. 10, the second embodiment is constructed from an imageinput device 1, a device-independent color conversion unit 4, a devicevalue conversion unit 5, an image output device 2, and an informationdatabase 54.

The device-independent color conversion unit 4 converts the image of asubject shot by the image input device 1 to a device-independent colorimage by referencing an input profile 4 a. The device value conversionunit 5 converts the resulting device-independent color image to devicevalues that suit the characteristics of the image output device 2 byreferencing an output profile 5 a, thereby producing an output image.The output image is outputted (displayed or printed) by the image outputdevice 2. Such image input device information and environmentalinformation as described previously are entered into the database 54,thus allowing the image input device information or environmentalinformation to be referenced freely at the time of creating the inputprofile.

Thus, in any environment an input image can be converted to adevice-independent color image. The information database may be retainedat the other end of the network, or on a storage medium, such as aCD-ROM, and, at the time of input profile creation, called forreference. An information database for information concerning the imageoutput device may be provided for reference at the time of creating theoutput profile. Thus, a device-independent color image can be convertedto an output image in any environment.

A third embodiment of the color reproduction device of the presentinvention will be described next with reference to FIGS. 11 and 12.

In the third embodiment, an input image itself has part of image inputdevice information or environmental information needed to create aninput profile, and color conversions are made on image data having adata structure that allows lighting conversion.

The third embodiment is constructed, as shown in FIG. 11, from an imageinput device 1, a color correction preprocessing unit 3 c, a colorcorrection unit 3 d, and an image output device 2.

Upon receipt of an image of a subject shot by the image input device 1,color correction preprocessing unit 3 c combines the input image dataand various information necessary for creation of an input profile intoan image format that allows color corrections on changes in color due tothe effect of lighting, the image format being referred to as thelighting convertible image format. The color correction unit 3 d causesinput and output profiles to operate on the lighting convertible imagedata 55 from the preprocessing unit 3 c to produce color-corrected imagedata, which, in turn, is outputted (displayed or printed) from the imageoutput device 2.

The color correction unit 3 d is composed of an input data division unit59, a device-independent color conversion unit 4, and a device valueconversion unit 5.

The input data division unit 59 divides input lighting convertible imagedata 55 into image data and various information necessary for inputprofile creation, which are then applied to the device-independent colorconversion unit 4. The conversion unit causes the input profile tooperate on the image data to output a device-independent color image.The device value conversion unit 5 converts the device-independent colorimage to device values that match the characteristics of the outputdevice by referencing the output profile.

The device-independent color conversion unit 4 comprises an inputprofile creation section 6 responsive to the image input deviceinformation and the environmental information for creating an inputprofile, and an input profile operation section 7 for causing the inputprofile to operate on the input image data for conversion to adevice-independent color image.

For example, as shown in FIG. 12, the lighting convertible image data 55comprises image data 55 a, a plurality of images assigned to bandnumbers, shooting-time lighting data 55 b as environmental information,filter information 55 c 1 and shutter speed information 55 c 2 used inthe image input device as image input device information, and headerinformation 55 d.

In this arrangement, image data itself inputted to thedevice-independent color conversion section 4 contains part of the imageinput device information and environmental information. Image inputdevice information and environmental information which are not containedin the input image data are externally applied to the conversion section4 as in the previous embodiments.

Therefore, by combining image data and part of image input deviceinformation and environmental information in the color correctionpreprocessing section 3 c into a single data structure, data can beobtained which allows observation-time lighting to be changed freely.Such an arrangement as shown in FIG. 8 may be used in place of thedevice-independent color conversion section 4 and the device valueconversion section 5.

FIGS. 13 and 14 show a modification of the third embodiment.

In this modification, the color correction section shown in FIG. 7 isseparated into a preprocessing section and a postprocessing section.Between the preprocessing and postprocessing sections, image data isconverted into an image data format (this is also the lightingconvertible image format) that approximates the spectral reflectance ofa subject for subsequent movement or transmission.

This modification is constructed from an image input device for shootinga subject to produce a subject image, a color correction preprocessingsection 3 e having an image format conversion section 56 for convertingthe input image into image data (lighting convertible image) thatapproximates the spectral reflectance of the subject by referencing aninput profile A 57 and adding header information to the image data, acolor correction section 3 f having a device-independent color imageconversion section 4 for converting lighting convertible image data 58comprising the image data and the header information into adevice-independent color image by referencing an input profile B 4 a anda device value conversion section 5 for converting the resultingdevice-independent color image to device values that match thecharacteristics of the image output device 2 by referencing an outputprofile 5 a to provide an output image, and an image output device 3 foroutputting (displaying or printing) the output image.

This color reproduction device is characterized by converting the formatof an input image so as to contain shooting characteristics andshooting-time lighting data to thereby provide a lighting convertibledata structure that approximates the spectral reflectance of a subject.

As an example of lighting convertible image data 58 represented by thelighting convertible image format, there is illustrated in FIG. 14 aformat of image data representing the spectral reflectance of a subject.

By converting an input image to image data containing shootingcharacteristics and shooting-time lighting data (image dataapproximating the spectral reflectance of a subject) in the colorcorrection preprocessing section 3 e, this modifications allows dataquantity to be reduced as compared with the image data format of FIG. 11in the third embodiment, thus increasing the processing speed.

Next, specific arrangements of the third embodiment will be described.

FIGS. 15 and 16 show a first specific arrangement of the thirdembodiment.

To confirm color samples of a commodity using a personal computer, thisarrangement employs a storage medium that is recorded with image datapertaining to the commodity in a data format that allows changes inlighting and a database for various lighting data.

For example, on a CD-ROM 60 as the storage medium are retained commoditycatalog viewer software, a lighting database that contains informationconcerning lighting assumed to be installed in a place to view thecommodity, and image data pertaining to the commodity (lightingconvertible image data).

The arrangement comprises the CD-ROM 60 recorded with the commoditycatalog viewer software, the lighting database, and image datapertaining to the commodity in a data format allowing lighting changes,a personal computer 61 that runs the commodity catalogue viewersoftware, a lighting sensor 62 that detects lighting in the place wherethe personal computer is installed, and a monitor 63 for displaying animage from the personal computer.

The personal computer 61 contains an output profile select section 64that selects a suitable one out of a plurality of output profiles whichhave been set up in advance, an observation lighting select section 65responsive to the lighting database and a detected signal from thelighting sensor 62 for selectively outputting data necessary for colorcorrection, and a color correction section 66 that makes colorcorrections on the image data of the subject by referencing input andoutput profiles to provide an output image to the monitor. Thearrangement further includes a hard disk, a ROM, a RAM, and so on, whichare needed to run the viewer software.

The input profile may be created in the color correction section fromthe image data and data from the lighting database. Alternatively, theinput profile may have been created in advance and stored in a memory.

In this arrangement, the user loads the CD-ROM 60 into the personalcomputer 61, activates the commodity catalog viewer software, anddisplays the commodity catalog. At this point, lighting data is alsoretrieved from the lighting database. Thus, the user can view how thecommodity changes in color if it were placed under fluorescent lamp,incandescent lamp, or sunlight, and so on. Further, by attaching alighting sensor to the personal computer, it is also possible toreproduce the color of the commodity in the place where the personalcomputer is installed. In addition, an object movie that allows an imageto be viewed from various angles and image data that allows changes inlighting (lighting convertible image data) may be used in combination.

In this embodiment, a storage medium is used to provide image data;otherwise, the Internet may be used. The commodity is not limited toclothing. This embodiment is also effective in confirming the colors ofcosmetics, furniture, electrical appliances, pictures, and so on.

Next, a second specific example of the third embodiment will bedescribed with reference to FIGS. 17, 18 and 19.

As shown in FIG. 17, this arrangement includes a digital camera inaddition to the components of FIGS. 15 and 16. An image captured by thedigital camera is fit into image data pertaining to a commodity readfrom the CD-ROM and the user changes lighting freely.

The digital camera 67 is constructed, as shown in FIG. 18, from a lens68, an image pickup device 69 for converting an image obtained throughthe photoelectric effect into electrical signals, a signal processingunit 70 for processing image information consisting of the electricalsignals, a shooting characteristic storage unit 71 for storing theshooting characteristics of the camera, a lighting sensor 72 fordetecting the lighting at a shooting site, a shooting-time lighting datadetect unit 73 for processing a detected signal from the sensor, and amemory card 74 for storing the subject image data, the shootingcharacteristics, and the shooting-time lighting data. The memory card isremovably attached to the camera.

The color reproduction device is constructed from the CD-ROM 60 recordedwith the commodity catalog viewer software, the lighting database, andlighting convertible image data, the personal computer 61 for runningthe viewer software, the lighting sensor 62 for detecting the lightingat the personal computer installation, the memory card 74 recorded withimage data captured by the digital camera 67, a subject characteristicdatabase 76 for storing subject characteristic, and a private clothingdatabase 77. The databases 76 and 77 are retained on a hard disk.

The personal computer 61 includes, in addition to the components in thefirst specific arrangement, a subject designation section 78 fordesignating data corresponding to a subject in the subjectcharacteristic database 76, a color correction section 79 for makingcolor corrections on subject image data read from the memory card inaccordance with shooting-time lighting data and shooting characteristicswhich are also read from the memory card, and an image combining section80 for combining independently color-corrected images.

In the color reproduction device thus arranged, when the commoditycatalog viewer software is activated to display clothes, a portrait (67a) of the user shot by the digital camera 67 and the image of clothingcan be combined (67 b).

User can construct clothing database 77, which has image data of clothesuser owned. Using coordinate software together, user can simulatecoordination of clothes when user bought the new cloth in catalog.

In this embodiment, a storage medium is used to provide image data;instead, the Internet may be used. The commodity is not limited toclothing. This embodiment is also effective in confirming the colors ofcosmetics, furniture, electrical appliances, pictures, and so on.

Next, a fourth embodiment of the color reproduction device of thepresent invention will be described.

This embodiment comprises an image input device capable of determiningpart of environmental characteristics at the same time a subject isshot, color correction unit 3, and an image output device 2.

In FIG. 20 there is illustrated the arrangement of a multi-spectralcamera that captures an image of a subject and part of environmentalinformation at the same time.

In this arrangement, a beam of light collected by an objective lens 81is split by a beam splitter 82 into tow beams: one is directed onto aCCD 84 and the other is reflected by a mirror 83 onto a spectrometer 85.

The multi-spectral camera captures a plurality of spectral images whilerotating a turret 86, having a plurality of bandpass filters by means ofa motor 87.

While the spectral images are captured, the spectrometer 85 measures thespectrum of a certain spot on the subject a plurality of times to obtainthe statistical nature of the spectrum of the subject, which is sent toa subject characteristic calculation unit 88 b. That is, the image dataand the subject characteristics of the environmental information can becaptured simultaneously.

FIG. 22 shows a modification of the camera shown in FIG. 21.

In this camera, a spectrometer 59 is placed on top of the camera. Ashooting-time lighting data calculation unit 88 b calculatesshooting-time lighting data from spectral data obtained by thespectrometer 59. That is, according to this type of camera, image dataand shooting-time lighting data, which is part of environmentalinformation, can be captured at the same time.

In this embodiment, use may be made of a multi-spectral camera using aplurality of bandpass filters, a multi-spectral camera using avariable-wavelength filter made of liquid crystal, a multi-spectralcamera in which the optical path of a beam of light is divided by meansof a prism, or a digital camera.

A fifth embodiment of the color reproduction device of the presentinvention will be described hereinafter.

This embodiment is constructed from an image input device 1, adevice-independent color conversion unit 4, a device value conversionunit 5, and an image output device 2, which remain unchanged from thosedescribed so far.

The device-independent color conversion unit 4 converts an input imageinto a device-independent color image by referencing an input profile 4a, and the device value conversion unit 5 converts thedevice-independent color image to device values that match thecharacteristics of the image output device by referencing an outputprofile 5 a. An output image is outputted (displayed or printed) by theimage output device.

The image input device 1 that captures the image of a subject isequipped with a shooting information storage unit that stores all orpart of image input device information, which can be referenced freelyat the time of color correction.

In FIG. 22 there is illustrated a multi-spectral camera that serves asthe image input device 1.

The multi-spectral camera is constructed from an objective lens 81, alens controller 93 for drive controlling the lens, an image pickupdevice (CCD) 84, a rotating filter turret 86 comprising a plurality ofbandpass filters used in capturing images in different wavelength bands,a motor 87 for rotating the filter turret 86, a filter characteristicstorage unit (shooting characteristic storage unit) 90, provided foreach filter turret, for storing the characteristics of the filtersmounted, a filter characteristic read unit 91 for reading the filtercharacteristics, and a shooting characteristic converting section 92 forconverting lens information, shutter speed control and filtercharacteristics to shooting characteristics.

The filter characteristics are read into the filter characteristic readunit 91 each time the characteristics of filters mounted on the filterturret 86 or the filter turret is exchanged.

Information concerning the objective lens 81 is read from the lenscontroller 93. The filter characteristic information and the lensinformation are converted into shooting characteristic data in theshooting characteristic conversion unit 92, which, in turn, is sent tothe color reproduction device. Data to be stored in the camera maycontain the spectral sensitivity characteristics of the CCD 84.

The camera used in this embodiment may be a multi-spectral camera usinga plurality of bandpass filters, a multi-spectral camera using avariable-wavelength filter made of liquid crystal, a multi-spectralcamera in which the optical path of a beam of light is divided by meansof a prism, or a digital camera.

A sixth embodiment of the color reproduction device of the presentinvention will be described next.

The sixth embodiment is the same as the arrangement shown in FIG. 1except the device value conversion unit 5.

As shown in FIG. 23, the device value conversion section 5 comprises anoutput profile creation section 10 for creating an output profile 5 a inaccordance with input image output device information, an offsetsubtraction section 94 for subtracting offset from an inputdevice-independent color image, and an output profile operation section24 for performing a color conversion process on the output of the offsetsubtraction section by referencing the output profile 5 a.

Usually, offset light and environment light are added to an image beingdisplayed. $\begin{matrix}{\begin{pmatrix}X \\Y \\Z\end{pmatrix} = {{\begin{pmatrix}{{Xr}\quad\max} & {{Xg}\quad\max} & {{Xb}\quad\max} \\{{Yr}\quad\max} & {{Yg}\quad\max} & {{Yb}\quad\max} \\{{Zr}\quad\max} & {{Zg}\quad\max} & {{Zb}\quad\max}\end{pmatrix}\begin{pmatrix}{\gamma\quad{r\lbrack R\rbrack}} \\{\gamma\quad{g\lbrack G\rbrack}} \\{\gamma\quad{b\lbrack B\rbrack}}\end{pmatrix}} + \begin{pmatrix}X_{0} \\Y_{0} \\Z_{0}\end{pmatrix}}} & (8)\end{matrix}$

As can be seen from equation (8), the resulting X, Y, or Z value isrepresented by the corresponding RGB values plus a bias value (X0, Y0,or Z0).

Thus, only the bias values related to offset light and environment lightare measured and the bias values are subtracted from XYZ values inputtedto the profile. This process allows an output profile sought in darkroom to be used as it is; thus, much work is not needed to create anprofile. Specifically,

matrix transform $\begin{matrix}{\quad{{\begin{pmatrix}R^{\prime} \\G^{\prime} \\B^{\prime}\end{pmatrix} = {\begin{pmatrix}{{Xr}\quad\max} & {{Xg}\quad\max} & {{Xb}\quad\max} \\{{Yr}\quad\max} & {{Yg}\quad\max} & {{Yb}\quad\max} \\{{Zr}\quad\max} & {{Zg}\quad\max} & {{Zb}\quad\max}\end{pmatrix}^{- 1}\begin{pmatrix}{X - X_{0}} \\{Y - Y_{0}} \\{Z - Z_{0}}\end{pmatrix}}}{{gamma}\quad{correction}\quad\begin{matrix}{R = {\gamma\quad{r^{- 1}\left\lbrack R^{\prime} \right\rbrack}}} \\{G = {\gamma\quad{g^{- 1}\left\lbrack G^{\prime} \right\rbrack}}} \\{B = {\gamma\quad{b^{- 1}\left\lbrack B^{\prime} \right\rbrack}}}\end{matrix}}}} & (9)\end{matrix}$As indicated in this equation, it is only required to subtract the biasvalues (X0, Y0, Z0) from colors to be displayed before the outputprofile is operated on.

A seventh embodiment of the color reproduction device of the presentinvention will be described next.

Usually, monitor offset light and environment light are measuredseparately or simultaneously and then subtracted from XYZ values to bedisplayed. Let XYZ values associated with monitor offset light bedenoted by Ox, Oy, and Oz, and XYZ values associated with environmentlight be denoted by Lx, Ly, and Lz. Then, bias values X0, Y0, and Z0 aregiven byX ₀ =O _(x) +L _(x)Y ₀ =O _(y) +L _(y)Z ₀ =O _(z) +L _(z)  (10)

FIG. 24 is a conceptual diagram of the monitor screen surface.

FIGS. 25A, 25B and 25C illustrate arrangements for measuring bias valuesusing a chromaticity meter.

In the arrangement of FIG. 25A, to measure the XYZ values, Ox, Oy, Oz,associated with monitor offset light, a monitor and a chromaticity meterare installed in a dark room and chromaticity values are detected withthe power to the monitor turned on and monitor inputs set such thatR=G=B=0. In FIG. 25B, XYZ values, Lx, Ly, Lz, associated withenvironment light are measured. In FIG. 25C, bias values X0, Y0 and Z0are measured directly.

FIG. 26 shows the arrangement of the device value conversion unit ofFIG. 23 and its peripheral units.

The device value conversion unit 5 is constructed from subtracters 97 a,79 b, and 79 c, a matrix transform section 98, and gamma correctionsections 99 a, 99 b, and 99 c.

The subtracters 97 a, 79 b, 79 c subtract bias values X0, Y0, and Z0from input values X, Y, and Z, respectively. The bias values X0, Y0 andZ0 are represented by equation (10) on the basis of Lz, Ly and Lx valuesfrom storage 95 and Ox, Oy, and Oz values from storage 96. The matrixtransform section 98 performs matrix transformation on the resulting X,Y, and Z values using matrix coefficients read from coefficient storagein accordance with equation (9). The gamma correction sections 99 a, 99b and 99 c make gamma corrections on the matrix-transformed R′, G′, andB′, respectively. For the output profile storage, refer to FIG. 36.

In the case where bias values are obtained directly as shown in FIG.25C, a bias memory 100 is provided for storing these bias values. Forthe above subtraction processing, the bias values stored in this memoryare used as shown in FIG. 26C.

In this embodiment, since there is no need to change the output profile,it can be operated on very easily and fast.

An eighth embodiment of the color reproduction device of the presentinvention will be described next.

In this embodiment, a bias sensor is provided for detecting both ofmonitor offset light and environment light.

As shown in FIG. 27A, a chromaticity sensor 101 is brought into contactwith the monitor display screen to detect offset light. To detectenvironment light, as shown in FIG. 27B, an environment light detectingadapter 102 is attached to the sensor 101 and the sensor is mounted onthe top of the monitor.

In this case, since the chromaticity values obtained from the sensor arenot ones resulting from reflection from the monitor screen, these valuesare converted by the environment light calculation unit to XYZ values,Lx, Ly, and Lz, associated with environment light.

The monitor offset light becomes stabilized a short time after the powerhas been applied to the monitor. On the other hand, environment lightchanges very greatly, especially if outdoor light comes.

According to the arrangement of FIG. 27B, even if the environment lightchanges rapidly, the change can be detected momentarily, and stabilizedcolor reproduction can be implemented all the time.

FIGS. 28A and 28B show an arrangement of a chromaticity sensor capableof detecting both the offset light and the environment light. The sensoris provided with windows 103 a and 103 b which face each other and allowoffset light and environment light to pass through, respectively. On thewindow 103 b for environment light is mounted an environment lightdetecting adapter 102. Between the windows is placed a rotating mirror104 which bends light coming through a window to a chromaticity sensor105 placed underneath. By rotating the mirror 104, switching is madebetween offset light detection and environment light detection.

FIG. 28C shows a modification. This arrangement is equipped with amirror 107 between the windows and chromaticity sensor 105 and spectrumsensor 106 placed underneath, allowing concurrent detection of monitoroffset light and environment light. Since the spectrum of environmentlight can be detected, the detected data can be used as observation-timelighting data serving as environmental information necessary forcreating an input profile.

A ninth embodiment of the color reproduction device of the presentinvention will be described next.

As shown in FIG. 29, the ninth embodiment has a chromaticity metermounted on a hood for shielding the monitor from environment light.

If the effect of environment light is too great, it is impossible toperform accurate color reproduction irrespective of the above-describedprocessing for environment light and offset light. In a place whereaccurate color reproduction is a requirement, as in a medical site wherediseased parts must be identified accurately, a hood 109 will inevitablybe attached to a monitor 108 to remove the effect of environment light.

In this arrangement, therefore, a chromaticity meter 101 is attached tothe environment light shielding hood 109 to detect bias values.

In this arrangement, when a reset button 110 is pressed, an image ofR=G=B=0 is displayed on the monitor 108, so that bias values X0, Y0 andZ0 are measured with the chromaticity meter 101. The effect ofenvironment light is not only reduced by the use of the hood 109 butalso removed by the above-described processing, which allows accuratecolor reproduction.

This embodiment is arranged to detect the bias values at the time whenthe reset button 110 is pressed. Alternatively, an R=G=B=0 image may bedisplayed at all times on a portion of the monitor screen, for example,at its lower right portion, to always update the bias values inaccordance with variations in environment light.

Depending on the portion of the monitor screen, the bias values mayvary. In such a case, instead of the chromatically meter a cameracapable of measuring XYZ values may be attached to obtain bias valuesfor each of pixels on the monitor or for each block of pixels. Theresulting pixel- or block-dependent bias values are subtracted in thesubtracters 97. When the hood 109 is used, environment light is reducedat the upper portion of the monitor screen but its lower portion isstill affected by the environment light. In this case, if bias valuesthat depend on the position on the monitor screen are used, thenaccurate color reproduction will be performed throughout the monitorscreen.

Next, a tenth embodiment of the color reproduction device of the presentinvention will be described.

This embodiment eliminates the need for a chromaticity meter at profilecreation time by preparing information necessary for profile creationbeforehand within the monitor.

As shown in FIG. 30, the monitor 110 is equipped with a time measurementunit 111 for measuring the operating time of the monitor, a thermometer112 for measuring the temperature of the monitor, an RGB phosphor XYZvalue storage unit 113 for storing the XYZ chromaticity values of theRGB phosphors, and a tone curve data storage 114 for storing tone curvedata. There are further provided a contrast control 115 and a brightnesscontrol 116.

An output profile calculation unit 117 comprises a matrix coefficientcalculation unit 118 and a gamma correction calculation unit 119. Anoutput profile storage unit 120 comprises a matrix coefficient storageunit 121 and RGB gamma correction tables 122 a, 122 b and 122 c.

In the storage units in the monitor, RGB phosphor XYZ chromaticityvalues and tone curve data under various conditions are stored. Byreferring to selected XYZ chromaticity values and tone curve data, theoutput profile calculation unit provides matrix coefficients and gammacorrection values. The various conditions are the overall operating timeof the monitor since it was manufactured, the temperature, and contrastand brightness values.

This embodiment allows an output profile to be operated on very easilybecause it is created without using a chromaticity meter.

In this embodiment, the RGB phosphor XYZ chromaticity values and tonecurve data under various conditions are stored inside the monitor;otherwise, they may be stored as file data in a personal computer andread when necessary.

Next, an eleventh embodiment of the color reproduction device of thepresent invention will be described. This embodiment is described interms of a device value conversion unit for make corrections on biasvalues using tables in referencing an output profile.

The device value conversion unit, as shown in FIG. 31, comprises RGBtables 123, 124, and 125 each serving as an output profile andsubtracters 126 for subtracting bias values X0, Y0 and Z0 from input XYZvalues.

Thus, each of RGB values which correspond to input XYZ values can beoutputted in accordance with the output profile in the correspondingtable.

This embodiment and the seventh embodiment are effective for monitorsthat satisfy equation (11). Some monitors do not satisfy equation (11).

For such monitors, a known method is effective which stores RGB valuescorresponding XYZ values in tables. The bias values are corrected by, asin the seventh embodiment, subtracting bias values X0, Y0 and Z0 from X,Y, and Z values and then referencing the tables.

This embodiment, while using tables in referencing output profiles, cancorrect bias values associated with offset light and environment lightwell.

As described so far, the color reproduction devices of the presentinvention makes image conversion with reference to image input deviceinformation, and color reproduction environmental information comprisingshooting-time and observation-time lighting spectral data, andinformation concerning the statistical nature of spectrum of a subject,and allows an output profile to be operated on an input image at highspeed even when offset light and environment light vary, therebyachieving accurate color reproduction. Also, an image captured by animage input device can be reproduced at a remote reproduction site.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A color-reproduction device for accurately achieving colorreproduction with an image output device for displaying an imagecorresponding to an input signal value, said color reproduction devicecomprising: bias-value storing means for storing a chromaticity value ofoffset light of the image output device and a chromaticity value ofenvironment light which is incident on a display surface of the imageoutput device; and subtracting means for subtracting, from achromaticity value corresponding to the input signal value, thechromaticity value of the offset light stored in the bias-value storingmeans and the chromaticity value of the environment light stored in thebias-value storing means.
 2. The color reproduction device according toclaim 1, wherein the chromaticity value of the offset light stored inthe bias-value storing means is a chromaticity value which is obtainedby sensing the display surface of the image output device with achromaticity value detection sensor, while the image output device andthe chromaticity value detection sensor are placed in a darkroom, andwherein a power supply of the image output device is turned on when theinput signal value is zero.
 3. The color reproduction device accordingto claim 2, wherein the chromaticity value detection sensor is adaptedto measure spectrum data.
 4. The color reproduction device according toclaim 1, wherein the chromaticity value of the environment light storedin the bias-value storing means is a chromaticity value which isobtained by sensing the display surface of the image output device witha chromaticity value detection sensor, while illumination light isincident on the display surface of the image output device, and while apower supply of the image output device is turned off.
 5. The colorreproduction device according to claim 4, wherein the chromaticity valuedetection sensor is adapted to measure spectrum data.
 6. The colorreproduction device according to claim 1, wherein the input signal valueis a chromaticity value obtained by adding the chromaticity value of theoffset light and the chromaticity value of the environment light to aninput value, and wherein a bias value stored in the bias-value storingmeans is a chromaticity value which is obtained by sensing the displaysurface of the image output device with a chromaticity value detectionsensor, while illumination light is incident on the display surface ofthe image output device, and wherein a power supply of the image outputdevice is turned on when the input signal value is zero.
 7. The colorreproduction device according to claim 6, wherein the chromaticity valuedetection sensor detects the chromaticity value of the environment lightstored in the bias-value storing means via an environment lightdetection adaptor which is attached to the chromaticity value detectionsensor.
 8. The color reproduction device according to claim 6, wherein:the chromaticity value detection sensor detects the chromaticity valueof the environment light stored in the bias-value storing means and thechromaticity value of the offset light stored in the bias-value storingmeans and is stored in a same casing; an optical axis of an opticalsystem in the casing is switched by a rotating mirror; and thechromaticity value detection sensor detects the chromaticity value ofthe environment light via an environment detection adaptor.
 9. The colorreproduction device according to claim 6, wherein: the chromaticityvalue detection sensor detects the chromaticity value of the offsetlight stored in the bias-value storing means; another chromaticity valuedetection sensor for detecting the chromaticity value of the environmentlight stored in the bias-value storing means is provided in a samehousing as the chromaticity value detection sensor for detecting thechromaticity value of the offset light stored in the bias-value storingmeans; an optical system in the housing includes two optical axesreflected by a mirror; and a direction from which the chromaticity valueof the offset light is detected is opposite to a direction from whichthe chromaticity value of the environment light is detected.
 10. Thecolor reproduction device according to claim 6, wherein the chromaticityvalue detection sensor is adapted to measure spectrum data.
 11. Acolor-reproduction device for accurately achieving color reproductionwith an image output device for displaying an image corresponding to aninput signal value, said color reproduction device comprising:bias-value storing means for storing a chromaticity value of environmentlight which is incident on a display surface of the image output device;and subtracting means for subtracting, from a chromaticity valuecorresponding to the input signal value, the chromaticity value of theenvironment light stored in the bias-value storing means.
 12. The colorreproduction device according to claim 11, wherein the chromaticityvalue of the environment light stored in the bias-value storing means isa chromaticity value which is obtained by sensing the display surface ofthe image output device with a chromaticity value detection sensor,while illumination light is incident on the display surface of the imageoutput device, and while a power supply of the image output device isturned off.